3.1. Contents of Heavy Metals in Animal Feeds
Results of the feed sample analyses on a dry matter (dm) basis from farms of different herd size are listed by livestock type in
Table 2,
Table 3,
Table 4. Contents of Pb are not reported here as its values were lower than the detection limit in all feed samples. All feed samples contained Cu, Zn and As, indicating that these additives were widely applied in animal production in Northeast China. Cr in cattle feeds was almost below the detection limit; while Cr was detected in over 13% of pig feeds and 20% of chicken feeds. Although Cd is not necessary for animal growth, over 60.6% of feed samples were detected to contain this toxic metal in the survey.
Table 2.
Heavy metals in cattle feed from farms of different herd size (mg/kg dm).
Table 2.
Heavy metals in cattle feed from farms of different herd size (mg/kg dm).
Herd size | No. of farms | Metals | Cu 1 | Zn 1 | As 2 | Cr 2 | Cd 2 |
---|
<100 | 11 | Range | 2.73–114.68 | 24.62–346.12 | 0.05–2.81 | nd–0.05 | nd–23.25 |
Mean | 32.12 a | 156.28 a | 1.38 a | nd a | 2.31 a |
Median | 19.08 | 119.32 | 1.49 | nd | 0.30 |
100–300 | 11 | Range | 2.73–61.48 | 26.27–215.92 | 0.44–2.42 | nd | nd–1.00 |
Mean | 15.74 a | 101.78 a | 1.18 a | nda | 0.38 a |
Median | 8.53 | 112.62 | 1.28 | nd | 0.35 |
>300 | 17 | Range | 4.58–113.14 | 11.07–334.86 | 0.01–6.12 | nd | nd-13.23 |
Mean | 25.98 a | 114.90 a | 0.80 b | nd a | 2.03 a |
Median | 13.63 | 91.00 | 0.41 | nd | 0.03 |
Table 3.
Heavy metals in chicken feed from farms of different herd size (mg/kg dm).
Table 3.
Heavy metals in chicken feed from farms of different herd size (mg/kg dm).
Herd size | No. of farms | Metals | Cu 1 | Zn 1 | As 1 | Cr 2 | Cd 2 |
---|
<2,000 | 6 | Range | 2.88–10.28 | 52.62–111.12 | 0.08–1.91 | nd–39.80 | nd |
Mean | 6.28 a | 74.91 b | 0.59 a | 6.63 a | nd a |
Median | 5.93 | 72.62 | 0.12 | nd | nd |
2,000–20,000 | 14 | Range | 2.88–51.73 | 63.12–127.32 | 0.04–3.36 | nd–936.45 | nd–1.70 |
Mean | 16.75 a | 89.34 ab | 0.75 a | 66.96 a | 0.26 a |
Median | 10.73 | 81.35 | 0.49 | nd | 0.13 |
>20,000 | 10 | Range | 4.47–98.08 | 74.07–150.97 | 0.02–6.42 | nd–160.25 | nd–8.00 |
Mean | 21.87 a | 103.72 a | 1.22 a | 25.72 a | 1.03 a |
Median | 13.43 | 104.46 | 0.68 | nd | 0.16 |
Table 4.
Heavy metals in pig feeds from farms of different herd size (mg/kg dm).
Table 4.
Heavy metals in pig feeds from farms of different herd size (mg/kg dm).
Herd size | No. of farms | Metals | Cu 2 | Zn 1 | As 1 | Cr 2 | Cd 2 |
---|
<200 | 7 | Range | 32.33–1,137.07 | 57.27–598.32 | 0.04–13.03 | nd–1.35 | nd–31.65 |
Mean | 343.38 a | 238.91 a | 5.62 a | 0.23 a | 8.73 a |
Median | 107.28 | 122.42 | 1.60 | nd | 1.02 |
200–800 | 7 | Range | 10.78–164.08 | 38.92–128.12 | 0.07–2.68 | nd–11.7 | nd–0.35 |
Mean | 93.92 a | 88.00 a | 1.00 a | 1.62 a | 0.18 a |
Median | 90.43 | 95.92 | 0.65 | nd | 0.25 |
>800 | 21 | Range | 2.33–258.08 | 37.37–206.72 | 0.02–10.95 | nd | nd–27.60 |
Mean | 117.70 a | 135.88 a | 2.22 a | nd a | 3.70 a |
Median | 119.88 | 138.37 | 1.08 | nd | 0.04 |
The contents of Cu, Zn, As and Cd in all cattle feed samples were in the ranges of 2.73–114.68 mg/kg, 11.07–346.12 mg/kg, 0.01–6.123 mg/kg and non-detectable (nd)–23.25 mg/kg. The metals of highest contents in cattle feeds from large farms were Zn and Cu, with mean contents of 114.90 mg/kg and 25.98 mg/kg, respectively. No significant difference was observed in the average contents of same heavy metal in cattle feeds from farms of different herd size except for As. In this survey, more As was found in cattle feeds from small farms than middle and large farms.
Cr was one of the most variable elements in all chicken feed samples, with a wide range between non-detectable (nd) to 936.45 mg/kg. Contents of Cd and As were <8 mg/kg in all the compound feeds analyzed. Contents of Cu in chicken feeds were typically in the range of 2.88–98.08 mg/kg, whilst Zn contents ranged from 52.62 to 150.97 mg/kg. In terms to the mean content, chicken feeds from large farms contained significantly higher Zn than that from small farms (p < 0.05, Tukey test).
The contents of Cu, Zn, As and Cd in all pig feed samples covered a wide range, 2.3–1,137.1 mg/kg, 37.37–598.32 mg/kg, 0.02–13.03 mg/kg and non-detectable (nd)–31.65 mg/kg. Like cattle feeds, the metals of highest contents in pig feeds were also Zn and Cu. With respect to average content, pig feeds contained higher Cu than cattle and chicken feeds. There was no significant difference in the average contents of the same heavy metal in pig feeds from farms of different herd size. However, the mean Cu in pig feeds from small farms was three and four times higher than those from middle and large farms, respectively.
3.2. Contents of Heavy Metals in Animal Manures
The contents of six heavy metals (Cu, Zn, As, Cr, Cd, Pb) in manures from different farms are shown in
Table 5,
Table 6,
Table 7. In cattle manures, the contents of Cu, Zn and As were 10.28–112.90 mg/kg, 16.97–377.17 mg/kg and 0.46–19.44 mg/kg, respectively. The contents of Cr, Cd and Pb in cattle manures were <11 mg/kg. The average contents of Cu, Zn, As, Cr, Cd and Pb in large farms were 31.37, 136.13, 2.71, 0.24, 0.73 and 2.68 mg/kg. Like the feeds, the metal of highest contents in cattle manure was Zn and Cu. Apart from Cd, there was no significant differences in the contents of heavy metal observed from farms of different herd size.
Table 5.
Heavy metals in cattle manure from farms of different herd size (mg/kg dm).
Table 5.
Heavy metals in cattle manure from farms of different herd size (mg/kg dm).
Herd size | No. of farms | Metals | Cu 1 | Zn 1 | As 1 | Cr 2 | Cd 2 | Pb 1 |
---|
<100 | 13 | Range | 14.08–58.78 | 33.82–224.12 | 0.73–4.65 | nd–3.60 | nd–3.60 | 0.63–3.23 |
Mean | 30.76 a | 119.12 a | 1.90 a | 1.30 a | 0.41 ab | 1.89 a |
Median | 30.93 | 113.60 | 1.51 | 0.90 | nd | 1.83 |
100–300 | 13 | Range | 19.48–66.58 | 65.27–319.27 | 0.65–5.98 | nd–2.97 | nd–1.80 | 1.03–4.68 |
Mean | 31.04 a | 126.33 a | 2.72 a | 1.09 a | 0.14 b | 2.24 a |
Median | 29.48 | 103.35 | 2.13 | 1.35 | nd | 1.68 |
>300 | 22 | Range | 10.28–112.90 | 16.97–377.17 | 0.46–19.44 | nd–1.05 | nd–10.49 | 0.53–5.48 |
Mean | 31.37 a | 136.13 a | 2.71 a | 0.24 a | 0.73 a | 2.68 a |
Median | 27.17 | 109.85 | 1.13 | nd | 0.21 | 2.81 |
Table 6.
Heavy metals in chicken manure from farms of different herd size (mg/kg dm).
Table 6.
Heavy metals in chicken manure from farms of different herd size (mg/kg dm).
Herd size | No. of farms | Metals | Cu 2 | Zn 2 | As 1 | Cr 2 | Cd 2 | Pb 2 |
---|
<2,000 | 8 | Range | 19.78–94.73 | 203.37–394.00 | 0.75–4.59 | nd–65.10 | nd–0.60 | nd–4.00 |
Mean | 51.60 a | 268.16 a | 2.69 a | 16.56 a | 0.08 a | 2.15 a |
Median | 43.56 | 251.97 | 2.73 | 4.20 | nd | 1.81 |
2,000–20,000 | 15 | Range | 1.53–101.93 | 15.37–367.92 | 0.68–6.59 | nd–2,402.95 | nd–6.10 | nd–19.93 |
Mean | 57.22 a | 241.74 a | 3.33 a | 224.79 a | 0.67 a | 4.89 a |
Median | 60.88 | 252.22 | 3.17 | 5.00 | nd | 2.78 |
>20,000 | 11 | Range | 21.83–487.43 | 152.17–1,063.32 | 0.55–10.42 | nd–150.1 | nd–37.99 | 0.68–22.10 |
Mean | 87.14 a | 384.15 a | 3.79 a | 23.71 a | 4.05 a | 4.44 a |
Median | 51.03 | 348.09 | 2.34 | 2.13 | nd | 2.26 |
Table 7.
Heavy metals in pig manure from farms of different herd size (mg/kg dm).
Table 7.
Heavy metals in pig manure from farms of different herd size (mg/kg dm).
Herd size | No. of farms | Metals | Cu 1 | Zn 1 | As 2 | Cr 2 | Cd 2 | Pb 1 |
---|
<200 | 8 | Range | 266.83–1,337.23 | 332.47–901.82 | 1.31–28.38 | nd–4.60 | nd–203.40 | 1.38–4.03 |
Mean | 958.79 a | 674.74 a | 6.19 a | 2.72 a | 46.12 a | 2.87 a |
Median | 1,095.65 | 737.40 | 1.91 | 3.59 | 0.05 | 2.84 |
200–800 | 9 | Range | 77.62–890.23 | 156.47–860.32 | 1.00–9.51 | nd–28.78 | nd–0.85 | 1.18–5.08 |
Mean | 420.39 b | 475.99 a | 4.61 a | 4.23 a | 0.10 a | 2.46 a |
Median | 516.73 | 486.17 | 3.39 | 1.10 | nd | 2.28 |
>800 | 19 | Range | 83.43–1,521.43 | 63.37–1,622.81 | 0.61–33.48 | nd–43.45 | nd–111.69 | nd–4.53 |
Mean | 612.23 b | 691.56 a | 11.75 a | 6.56 a | 8.38 a | 2.37 a |
Median | 609.02 | 721.43 | 9.94 | 0.95 | 0.26 | 2.53 |
In chicken manures, the contents of Cu, Zn, As, Pb and Cd ranged from 1.53–487.43 mg/kg, 15.37–1,063.32 mg/kg, 0.55–10.42 mg/kg, non-detectable (nd)–22.10 mg/kg and non-detectable (nd)-37.99 mg/kg, respectively. The contents of Cr in chicken manures displayed the widest range, from non-detectable (nd) to 2,402.95 mg/kg. The average contents of Cu, Zn, As, Cr, Cd and Pb in large farms were 87.14, 384.15, 3.79, 23.71, 4.05 and 4.44 mg/kg. There was no significant difference in the contents of heavy metal observed among manures from farms of different herd size.
In pig manures, the content range of Cu, Zn, As and Cr was 77.62–1,521.43 mg/kg, 63.37–1,622.81 mg/kg, 0.61–33.48 mg/kg and non-detectable (nd)–43.45 mg/kg, respectively. The contents of Cd also clearly featured a large range, from non-detectable (nd) to 111.69 mg/kg. The contents of Pb were typically <5 mg/kg. In large pig farms, the average contents of Zn, As, Cr and Cd in manure were 691.56, 11.75, 6.56 and 8.38 mg/kg, which were generally higher than that in small and middle farms. However, the average content of Cu in manures of small pig farms was significantly higher than that of middle and large farms (p < 0.05). The contents of Pb in manures showed comparable values in farms of different herd size.